A large number of LSI chips which are highly integrated are used to raise the performance of personal computers, cellular phones, mobile machines represented by personal digital assistants (PDAs), digital audio/visual (AV) equipment, and the like that support information-oriented society. A packaging technique that allows such LSI chips to be densely mounted and driven at high speed is being demanded since conventional packaging technologies which use electric connections alone have reached the limit in solving such problems as transmission delay and crosstalk and in reducing electromagnetic interference (EMI). Against this background, a system that uses optical connection in combination with electric connection is being considered.
Several cases of optically interconnecting chips have been proposed. One of those cases is a system in which a slab waveguide is formed from an organic polymer on a flat substrate and is used as a transmission medium. This system supposedly has advantages over a system in which a linear optical waveguide is elaborated, such as having better compatibility with LSI chips and with boards or packages for mounting LSI chips, being easier to manufacture, and allowing chips to interconnect freely. An example of this case is disclosed in JP 08-293836 A. A structural example thereof is shown in FIG. 9. A substrate 201′ is equipped with an optical waveguide layer that is sealed with a polymer sealing material 209. An insulating layer 208 of the substrate 201′ has transmitter elements 204 and 206 and a receiver element 205. An LSI board 202 is mounted to achieve signal transmission between LSIs through a slab optical waveguide 201″ (signal light 203). A hologram 207 is used to optically couple the transmitter elements 204 and 206, the receiver element 205, and the waveguide 201″ to one another, and a wavelength-controlling element controls the state of coupling between the elements.
However, the above method, which uses a wavelength-controlling element to control connection between LSI chips, requires the receiver element and the wavelength-controlling element to be highly stable and therefore is difficult to carry out in the vicinity of LSIs where the temperature environment is not always appropriate.
On the other hand, U.S. Pat. No. 5,191,219 discloses the following information processing apparatus. That is, the information processing apparatus comprises means forming a planar optical waveguide which extends in two dimensions and serves as a shared medium, a plurality of light-emitting means and a plurality of light-detecting means extending in a two dimensional arrangement over said planar optical waveguide for broadcasting light signals and abstracting light signals, respectively, into and from said planar optical waveguide, and a plurality of subsystems including input and output ports for processing the light signals in the shared medium, the light-detecting means being coupled to input ports and the light-emitting means being coupled to output ports of the subsystems.
The United States patent discloses the optical connection, but is not much flexible in forming an optical connection.